1. Field of the Invention
The invention relates to a power tracking device, and more particularly to a power tracking device for identifying a maximum power point of a power generation apparatus.
2. Description of the Related Art
Power generation apparatuses, such as photovoltaic power generators, wind power generators, and heat power generators etc., are widely used in various systems. Conversion efficiency of a power generation apparatus is dependant on the conditions of both the load and energy source of the power generation apparatus. The energy source of a power generation apparatus may not be stable (e.g. wind power or solar power levels may vary) and a load of a power generation apparatus may also vary. Thus, dynamic control techniques are applied to power generation apparatuses to obtain maximum conversion efficiency of the power generation apparatuses.
FIG. 1 shows a diagram illustrating a relationship between voltage and current of an output power of a power generation apparatus. In FIG. 1, curve S1 represents the current/voltage curve of the output power at lower temperature, curve S2 represents the current/voltage curve of the output power at middle temperature, and curve S3 represents the current/voltage curve of the output power at higher temperature. As shown by the curves S1, S2 or S3, when the value of the current of the output power is maximized, the voltage level of the output power tends is minimized, and vice versa. Furthermore, curve S4 represents the output power according to the voltage at lower temperature, curve S5 represents the output power according to the voltage at middle temperature, and curve S6 represents the output power according to the voltage at higher temperature. Thus, the maximum power points of the curves S4, S5 and S6 are different. Namely, different conditions will affect the maximum power point for the power generation apparatus, such as variations in wind force, light density, temperature, load, and so on. In order to obtain the maximum conversion efficiency for a power generation apparatus, a tracking technique is required to track the power level of the power generation apparatus, to identify the maximum power point and transfer the maximum output power from the power generation apparatus to the load.
Typically, a maximum power point for a power generation apparatus may be identified by measuring and comparing the voltage and the current from the power generation apparatus. However, there are many possible voltage/current points which may be detected, as shown in the curves of FIG. 1. Thus, identifying a maximum power point by the measuring and comparing of voltage/current technique is complex and inefficient.
Furthermore, an analog to digital converter (ADC) is used to sample the voltage and the current from a power generation apparatus and/or from a load and then process the sampled voltage and the sampled current digitally. Next, a digital to analog converter (DAC) is used to convert the computed digital signals to analog signals, so as to output the analog signal to a pulse width modulation (PWM) device for power control. While digital processes may be flexible when implementing maximum power point tracking, however, tracking efficiency thereof is limited by the resolution and conversion speed of the ADC and the DAC used, as well as computing power. Meanwhile, if a high resolution, high conversion speed or high computing power ADC and DAC is used, required area increases along with costs.
Therefore, a power tracking device for a power generation apparatus is desired, which simply, quickly, flexibly, and inexpensively identifies a maximum power point of a power generation apparatus.